The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The leading edges of aircraft, in particular the front lips of the air inlets of turbojet engine nacelles forming rounded flanges turned forwards, may show, under some weather conditions such as the crossing of clouds with a low temperature, the formation of frost which ends up constituting blocks of ice.
Thus, a modification of the aerodynamic profile of the nacelle is obtained, which may disturb the air supply and the proper operation of the engine, and the performance of this engine is decreased. In addition, a detachment of blocks of ice which enter inside the turbojet engine and damage fan blades, may result. Flight authorizations under icing conditions require the presence of a de-icing system.
A known type of de-icing or anti-icing systems, presented in particular in the documents EP-B1-0913326 or US-A1-20020179773, includes a circular tube surrounding the nacelle, which supplies with hot air collected on the turbojet engine, the internal volume of the front lip of this nacelle in order to heat its external walls.
Moreover, in order to reduce the acoustic emissions of the turbojet engines, some internal walls of the nacelle are fitted with sandwich panels including a central core presenting honeycomb-shaped cells, which is covered by a tight internal rear skin, and by an external front skin turned toward the sound source, which is perforated or porous.
Thus, the open cells constitute a Helmholtz resonator type device, which contributes to significantly reduce the acoustic emissions.
The central core of the sandwich panel may include one single thickness of cells, or two thicknesses separated by a micro-perforated medial skin, so as to improve the acoustic performance of the panel.
In particular, this type of acoustic panel is disposed on the internal walls of the annular cold air flow path, in the case of a bypass turbojet engine, as well as on the internal wall of the upstream air inlet.
In particular, in the documents of the prior art disclosed hereinabove, the radially inner surfaces of the leading edge lip, turned toward the axis of the nacelle, are fitted starting from the front of the lip, with this type of acoustic panels. It will be noted that fitting as far upstream as possible from the air inlet of the nacelle, in particular in the substantially cylindrical internal volume, gives improved acoustic performances of this nacelle.
Nonetheless, as the acoustic panels constitute a thermal insulator, small perforations are then made on the internal skin of these panels, in order to obtain a hot air flow rate which passes through the panels so as to heat the external wall from the air circulating inside this lip.
However, this method poses different problems, in particular the required hot air flow rate is hardly compatible with the acceptable perforation of the internal skin, and the acoustic performance of these panels is reduced.
In addition, a loss of the aerodynamic efficiency of the nacelle is obtained, in particular with a bailer effect where the external air enters inside the first upstream cells passing through the acoustic panel, arriving in the internal volume of the lip, and then coming out via the last downstream cells by passing again through this panel.